Various configurations of aspirated smoke detectors are known to be useful in harsh environments, where maintenance can be difficult or where aesthetics matter. Several embodiments thereof are disclosed in Griffith et al., U.S. Pat. No. 7,669,457, entitled “Apparatus and Method of Smoke Detection”. The '457 patent issued Mar. 2, 2010, is assigned to the assignee hereof, and is incorporated herein by reference.
When the installation of an aspirating smoke detector and associated conduit or pipe network is performed, it is necessary and required that the installer measure the transport time of the installed apparatus. This measurement is performed to verify that one of the core parts of the installation, the pipe network, has been correctly installed.
Transport time is the time for air/smoke to flow from a sampling point to the smoke sensing element in the aspirating device. The transport time will preferably not include any processing time and is specifically limited to the time it takes to transport air/smoke from the sampling point to the sensing element.
The theoretical transport time can be estimated by software tools. The installer compares software results with the measured transport time to verify that, in the real system, there are no pipe leakages, errors in setup of the device, issues with a fan, incorrect pipe assembly, etc.
The typical way that installers measure transport time in a real system is to use smoke pellets or cotton wicks to produce smoke to flow into a selected opening or hole of the pipe network connected to the aspirated detector. The transport time is measured as the time between the start of smoke inflow and the signaling of the presence of smoke at the aspirated device. The device is set to the highest level of sensibility.
The measured time is not the transport time as defined. It is the transport time plus the processing time to respond to inflowing smoke, which depends on the characteristics of the sensing element and associated alarm/filtering algorithms. The problem is that the processing time is difficult to calculate because it may vary from one test to another, due, for example, to unknown polling intervals, and, with time, due to changes in the alarm threshold. This additional time causes an inaccurate and non-reproducible determination of the transport time, affecting the verification of the system. It would be desirable to eliminate these inaccuracies.